Both paints were latex. The one the contractor used was a brand I never heard of, "Super Craft" and it says industrial/commercial on the label; it's a flat latex. I used Behr semigloss latex over this. My bathroom does not have a humidity problem. It has a window and I always leave it open a crack. I've never noticed peeling problems before this.
Do you think it was the quality of the "Super Craft" the contractor used? Or the "Behr" paint? I didn't put it on particularly thick; I've painted rooms many times in the past. This is the first time this has every happened.